title: Reducing ambulance diversion at hospital and regional levels: systemic review of insights from simulation models.
abstract: BACKGROUND
  Optimal solutions for reducing diversion without worsening emergency department (ED) crowding are unclear. We performed a systematic review of published simulation studies to identify: 1) the tradeoff between ambulance diversion and ED wait times; 2) the predicted impact of patient flow interventions on reducing diversion; and 3) the optimal regional strategy for reducing diversion.
  
  
  METHODS
  
  
  
  METHODS
  Systematic review of articles using MEDLINE, Inspec, Scopus. Additional studies identified through bibliography review, Google Scholar, and scientific conference proceedings.
  
  
  METHODS
  Only simulations modeling ambulance diversion as a result of ED crowding or inpatient capacity problems were included.
  
  
  METHODS
  Independent extraction by two authors using predefined data fields.
  
  
  RESULTS
  We identified 5,116 potentially relevant records; 10 studies met inclusion criteria. In models that quantified the relationship between ED throughput times and diversion, diversion was found to only minimally improve ED waiting room times. Adding holding units for inpatient boarders and ED-based fast tracks, improving lab turnaround times, and smoothing elective surgery caseloads were found to reduce diversion considerably. While two models found a cooperative agreement between hospitals is necessary to prevent defensive diversion behavior by a hospital when a nearby hospital goes on diversion, one model found there may be more optimal solutions for reducing region wide wait times than a regional ban on diversion.
  
  
  CONCLUSIONS
  Smoothing elective surgery caseloads, adding ED fast tracks as well as holding units for inpatient boarders, improving ED lab turnaround times, and implementing regional cooperative agreements among hospitals are promising avenues for reducing diversion.
authors.affiliation: Stanford University, Division of Emergency Medicine, Stanford, California.
authors.forename: M Kit
authors.initials: MK
authors.lastname: Delgado
authors.forename: Lesley J
authors.initials: LJ
authors.lastname: Meng
authors.forename: Mary P
authors.initials: MP
authors.lastname: Mercer
authors.forename: Jesse M
authors.initials: JM
authors.lastname: Pines
authors.forename: Douglas K
authors.initials: DK
authors.lastname: Owens
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Zaric